A lithium ion secondary battery is widely practically used as a battery for compact electronic equipment such as a notebook personal computer and a cellular phone owing to its advantages such as a high energy density, small self-discharge and long-term reliability. At present, a carbon material and lithium cobalt oxide (LiCoO2) are generally used respectively as a negative electrode active material and a positive electrode active material of a lithium ion secondary battery, and lithium ion secondary batteries using these materials have been commercialized.
In recent years, however, electronic equipment has been increased in functionality and used in electric vehicles, and there is a demand for development of a lower cost and higher performance lithium ion secondary battery.
As for the negative electrode active material, a negative electrode active material containing silicon (Si) as a constituent element is being developed as a high-capacity material to be used instead of a carbon material.
As for the positive electrode active material, nickel-based and manganese-based materials are being developed from the viewpoint of cost and capacity. For example, a lithium manganese-based composite oxide having a layered rock-salt structure as a crystal structure is being examined.
Patent Literature 1 describes a negative electrode including a negative electrode active material layer containing a negative electrode active material containing silicon (Si) as a constituent element; and a coating layer covering the negative electrode active material layer and containing an oxide of a 3d transition metal element (at least one selected from the group consisting of iron (Fe), cobalt (Co) and nickel (Ni)). Patent Literature 1 discloses that a lithium ion secondary battery including this negative electrode can be improved in cyclability.
Patent Literature 2 describes a secondary battery including a positive electrode containing a positive electrode active material including a lithium transition metal oxide; a negative electrode including a negative electrode active material layer containing a negative electrode active material including a silicon-containing particle and a binding agent; and an electrolyte, in which the negative electrode active material layer further contains a transition metal-silicon alloy particle made of an alloy containing the same element as the transition metal (Mn, Fe or Ni) contained in the lithium transition metal oxide, and Si. Patent Literature 2 discloses that a transition metal ion eluted from the positive electrode active material is preferentially deposited on the transition metal-silicon alloy particle for suppressing deposition of the transition metal on the surface of the negative electrode active material in this secondary battery, so that the resistance change in a high-temperature cycle can be suppressed.
Patent Literature 3 describes a lithium ion secondary battery including a positive electrode containing a positive electrode active material made of a layered rock-salt structure lithium manganese-based composite oxide containing a lithium (Li) element and a tetravalent manganese (Mn) element; a negative electrode containing a negative electrode active material made of a silicon oxide represented by SiOx (0.3×1.6); and an electrolyte solution containing a solvent or a liquid dispersion medium, an electrolyte and an additive of a specific polycyclic hydrocarbon compound (such as biphenyl and cyclohexylbenzene). Patent Literature 3 discloses that this secondary battery is suppressed in deterioration of the charge/discharge capacity otherwise caused after storage.